1. Field of the Invention
The present invention relates to a thermosensitive recording medium which has sufficient antibacterial efficacy and is chemical-resistant, notably plasticizer-resistant, and superior in image residual rate. The present invention relates particularly to a thermosensitive recording medium suitable for use in the fields of medicine and food.
2. Description of the Related Art
In recent years, along with the diversification of information and the expansion of needs, a variety of types of recording materials have been studied, developed and put to practical use in the field of information recording. Among the recording materials, thermosensitive recording materials are advantageous, for example in that (1) simplified recording of images is enabled by a heating process alone, and (2) required apparatuses have simple mechanisms and can therefore be easily made compact and the recording materials are easy to handle and inexpensive. Accordingly, techniques for such recording materials are widely utilized, for example, in the fields of information processing (for output of desk calculators, computers, etc.), recorders for medical measurement, low-speed to high-speed facsimiles, automated ticket machines (for passenger tickets, admission tickets, etc.), thermosensitive copying, labels in the POS system, and tags.
A thermosensitive recording medium generally includes at least a support and a thermosensitive recording layer, and a thermosensitive recording adhesive label includes an adhesive layer and release paper in addition to a support and a thermosensitive recording layer. The release paper is obtained by coating polyethylene-laminated paper, clay-coated paper, high-density base paper such as glassine paper, etc. with a release agent such as a silicone compound or fluorine compound. Examples of an adhesive constituting the adhesive layer include hot-melt adhesives, solvent adhesives and emulsion adhesives such as rubber adhesives, acrylic adhesives and vinyl ether adhesives. Among these, acrylic emulsion adhesives, in particular, are widely used for their safety, quality and inexpensiveness.
Also, the thermosensitive recording medium is generally required to store a recorded image stably; accordingly, there have been proposed a method of coating the thermosensitive recording layer with an aqueous emulsion of a resin which is capable of forming a film and is chemical-resistant, and a method of coating the thermosensitive recording layer with a water-soluble polymer compound such as polyvinyl alcohol. As for the thermosensitive recording adhesive label, the adhesive layer and the release paper are provided on the back surface of the support; as described above, the adhesive constituting the adhesive layer is generally selected from rubber adhesives, acrylic adhesives and the like, particularly acrylic emulsion adhesives. Thus, a low-molecular-weight oligomer, a surfactant and the like contained in the adhesive layer may migrate to the thermosensitive recording layer while the thermosensitive recording adhesive label is stored for a long period of time, even before it starts being used as a label, thereby possibly causing such known problems that the recording sensitivity decreases, and the image density decreases when the label is chemical-resistant, particularly plasticizer-resistant.
Further, more and more antibacterial products, notably fiber and plastic antibacterial products, are becoming widely available, and they are widely utilized in a variety of fields, e.g. for bath-related uses, kitchen equipment, food-related uses, electric appliances, office machines, office equipment and medical uses. In food-related uses, in particular, the antibacterial products are expected to be used as discount-showing labels attached onto wrappings covering foamed trays for foods. In medical uses, the antibacterial products are expected to be used as labels attached onto blood collection tubes, infusion bottles and the like in an attempt to solve the serious problem of in-hospital infection. Also, there is a great problem with the disposal of materials which can be noxious sources of secondary infection, contained in medical waste discharged from medical institutions and the like.
Regarding labels with antibacterial agents, tapes for medical uses in which adhesive layers contain silver-based antibacterial agents have been proposed, (refer to Japanese Patent Application Laid-Open (JP-A) No. 2001-137279, for example). However, the silver-based antibacterial agents are not effective unless in contact with microorganisms such as bacteria, so that effects cannot be expected from the silver-based antibacterial agents without them being used near water.
Meanwhile, sheets which contain volatile antibacterial agents have been proposed (refer to JP-A Nos. 2005-120008 and 2007-68723, for example). However, when used as thermosensitive recording materials, they cannot be satisfactorily used because images recorded thereon by thermosensitive recording degrade with time.
Also, tapes and tack seals, in which organic antibacterial insecticides and/or inorganic antibacterial fungicides are mixed with adhesives have been proposed (refer to JP-A No. 2001-48710, for example). However, natural antibacterial agents are used therein, so that when they are used as thermosensitive recording materials, they cannot be satisfactorily used because images recorded thereon by thermosensitive recording degrade with time.
Meanwhile, inclusion of antibacterial agents based upon haloalkylthiophthalimide and/or chlorhexidine gluconate in thermosensitive recording media has been proposed (refer to JP-A Nos. 09-123602 and 11-58964, for example). However, thermosensitive recording layers decrease in sensitivity at high temperatures and high humidity.
Further, thermosensitive recording media which contain inorganic ion antibacterial agents have been proposed (refer to JP-A No. 09-95051, for example). However, effects cannot be expected from the thermosensitive recording media unless the antibacterial agents are in direct contact with microorganisms such as bacteria.
Also, dispersions or surface coating treatment agents, which contain inorganic antibacterial agents and imidazole antibacterial agents have been proposed (refer to JP-A No. 2007-211004, for example). However, the dispersions or the surface coating treatment agents contain organic solvents as their essential components, so that when used for thermosensitive recording materials, there is such a problem that fogging of background portions of images recorded by thermosensitive recording arises.